1. Field of the Invention
This invention relates broadly to the field of containers that are adapted to hold highly pressurized contents, such as aerosol mixtures, and more particularly to a blow molded plastic aerosol container having a finish portion that is constructed and arranged to provide maximum resistance to deformation and stress cracking at high internal pressures.
2. Description of the Related Technology
Aerosol containers have conventionally been fabricated from metal, and are conventionally formed as a cylindrical tube having upper and lower end closures. The bottom end closure is typically shaped as a concave dome, and the upper end closure typically includes a manually actuatable valve for dispensing the pressurized aerosol contents of the container.
Metallic containers have certain inherent disadvantages, such as a tendency to rust over time and to scratch surfaces with which they may come into contact.
Efforts have been made in the past to develop plastic aerosol containers, but have encountered difficulties, mainly relating to controlling the deformation of the plastic material as a result of the significant internal pressurization that is necessary in an aerosol container. Aerosol containers commonly require internal pressures of the magnitude of 50-300 psi, which is significantly greater than pressures that are typically encountered in other packaging applications for which plastic material has been used, such as the packaging of carbonated beverages. Accordingly, design considerations for plastic aerosol containers are quite different than they are for lower pressure packaging applications such as plastic beverage containers.
One common type of plastic container is fabricated from a material such as polyethylene terephthalate (PET) and is manufactured from an injection molded preform having a threaded finish portion using the reheat stretch blow molding process. While such containers hold some promise for aerosol applications, they are susceptible to stress cracking in the finish portion while under pressurization. In addition, the finish portion of such containers has a tendency to deform when the container is pressurized, possibly resulting in a loss of sealing integrity between the container and the aerosol dispensing closure.
A plastic aerosol container that utilizes a threaded finish portion also requires application of an aerosol dispensing closure to the finish portion at a torque that may be greater than that used for the application of closures to conventional, non-aerosol containers. Conventional capping machines may be unable to generate such torque without causing undesired rotation of the container.
A need exists for an improved blow molded plastic aerosol container that is less susceptible to stress cracking and deformation in the finish region than are conventional blow molded containers. A need also exists for a plastic aerosol container that can have an aerosol dispensing closure applied thereto at higher torques without rotation of the container.